PEALE.] GEOLOGY POTSDAM GROUP CANADIAN PEETOD. Ill 



identifying them as belonging to the Potsdam group. Afterward 

 Dr. Bavden found fossils in the same formation in the Big Horn range 

 in Dakota. In 1869* he also found, near Colorado City, fossils in layers 

 just above, that prove the layer in which they were found to belong to 

 the Calciferous or to the Quebec group. In the report for 1870, he also 

 mentions the group. 



In 1872 Dr. Hay den and myself recognised the same group in Mon- 

 tana, near Gallatin City, t The same year Professor Bradley t recog- 

 nized it in Utah, Idaho, and Wyoming. 



Newberry § speaks of the Potsdam sandstone occurring on the Colo- 

 rado Elver in Utah. Comstock|| refers to it as occurring in the Wind 

 Eiver Mountains. In all these localities, the general characters are 

 very similar. In Colorado, in 1873, I discovered Potsdam sandstone in 

 various localities, but was unable to discover any organic remains in it, 

 although just above, I found fossils referred by Professor Meek to the 

 Quebec group. Dr. Endlich, in 1873, had outcrops of the group in his 

 district, while the northern district was without any trace of it. 



During the past season I iound on Eagle Eiver a series of beds rest- 

 ing on the gneiss and schists. From their position and lithological rela- 

 tions to corresponding beds found by me in 1873, I referred the lower 

 layer to the Potsdam group. The characters of these beds will be given 

 in the sections a little farther on. Their extent in my district was 

 limited. 



JEagle River. — The Potsdam group here is represented by a bed of 

 white quartzite. Near the head of the river it is shown on both sides, 

 dipping to the northeast at an angle of 5° to 10°. It is between 300 

 and 400 feet in thickness. As we go down the river it caps the ridge 

 separating the two forks, while the gneissic rocks on the west side of 

 the western fork are bare, the quartzite which once extended over 

 them having been eroded away. Still farther along, opposite the canon, 

 they re-appear in patches, and soon extend from the edge of the caSon 

 in long strips between the branches of the Eagle, toward the Sawatch 

 range, as shown in Fig. 2, Plate I, representing the Potsdam sandstone 

 on the gneiss. The inclination is toward the northeast, the angle being 

 very small. At the point where the section in the illustration is made, 

 it is shown on both sides, but as we go down the river it gradually dis- 

 appears on tlie north, and appears only on the south side, where it con- 

 tinues to the southward, curving around the end of the Sawatch range. 

 The inclination increases, and consequently the area occupied by the 

 Potsdam becomes much narrower, connecting with the belt that extends 

 across Frying-Pan Creek into the Elk Mountains. 



Grand River. — The only place on the Grand where the Potsdam group 

 is likely to be seen is in the caiion between the mouth of the Eagle and 

 the mouth of Eoaring Fork. Mr. Marvine's report will treat of this. 



Gunnison River. — There is no exposure of this age on the Gunnison 

 in our district for 1874. 



CANADIAN PEEIOD — CALCIFEKOUS AND QUEBEC GROUPS. 



Although I cannot define the limits of the groups, in ascending from 

 the top of the Potsdam sandstone, I have thought it best to give them 



* Report United States Geological Survey, 1870, page 259. 



t Report United States Geological Survey, 1872, pages 72, 174. 



X Report United States Geological Survey, 1872. Report cf F. H. Bradley. 



II Ives's report of Colorado River ; page 47 of Geological Report. 



§ Report on Northwestern Wyoming, by William A. Jones, page 106, 



